I didn't know what to do with the timeline. Actionscript is complicated.

Flex is a developer friendly way to create flash apps with code. Programming style (tags + script) is familiar to web developers.
Uses MXML and CSS

Rich actionscript framework.
UI components
Effects and skins

SDK is free to download and you don't need to buy anything from adobe.

Shares some features with HTML and some with flash. Unlike HTML flex was designed for app development. (no more slicing up images to create a navbar)

Developing with Flex:

Using Flex-builder - going to create a Flickr Browser.
Behind the scenes code is generated as MXML

States allow you to set-up changes to the app.

E.g we have a base state for entering a flickr tag and a 100% view for the results.

Adding a click attribute to the MXML defining the button allows me to change between the states

To get the photos from Flickr I add the url to a "service" and then need to create a databinding to get the contents of the input.
The Tilelist (where the photos are displayed) has to be connected to the results returned by the server. I can use an itemRenderer which will provide thumbnailing.
I also add a call to the button to send the request to the server.

runs the app and shows images for the tag kikubird returned from Flickr.

Example Flex Apps.

Picnik
Photoediting Tool

To enable flex 2 we needed to do a lot of work behind the scenes on Flash.
It's a Virtual Machine which runs the actionscript code.
Uses JIT compilation.